The events of Sep. 11, 2001 instigated an urgency for more effective and stringent screening of airport baggage. The urgency for security expanded from an inspection of carry-on bags for knives and guns to a complete inspection of checked bags for a range of hazards with particular emphasis upon concealed explosives. X-ray imaging is a widespread technology currently employed for screening.
Identification systems based on X-ray diffraction (XRD) techniques provide an improved discrimination of the materials compared to that provided by the X-ray baggage scanners. The XRD identification systems measure d-spacings between lattice planes of micro-crystals in the materials. A “d-spacing” is a perpendicular distance between adjacent lattice planes in any of the materials.
However, the XRD identification systems for explosives detection and baggage scanning are not yet highly developed. Moreover, the diffraction techniques suffer from a false alarm problem for some classes of substances. There are certain types of explosives in which an explosive component cannot be identified by the XRD identification systems and the lack of identification leads to a high false alarm rate.